I. Field of the Present Invention
The present invention relates generally to throttle body constructions including a throttle valve, and more particularly to a throttle passage profile for adjusting the change in rate of fluid flow through the throttle passage throughout a range of valve travel.
II. Description of the Prior Art
Throttle bodies including a passage through which the flow of air or a fuel-air mixture is controlled by angular variation of a throttle valve are well known. Typically, the throttle valve is a butterfly valve formed by a plate pivoted about an axis perpendicular to the longitudinal axis of the passage. The angular position of the plate varies in response to a throttle control mechanism. Typically, the actuator for the throttle control mechanism includes an accelerator pedal mounted for access to the vehicle operator within the vehicle passenger compartment. In a closed throttle position, the throttle valve plate is positioned to engage the periphery of the throttle body passage and close off flow through the throttle body. As the actuator i.e. accelerator pedal, is displaced, the control mechanism varies the angular position of the plate so as to increase the area through which fluid may flow through the throttle body passage.
It may be appreciated that the rate of change of the flow through the throttle passage varies throughout the angular variation of the throttle plate as a function of the area of the throttle passage which is obstructed by the throttle plate at the various angular positions of the plate. However, initial rate of change of the flow through the throttle body passage from a closed throttle plate position in response to actuation of the accelerator pedal is greater than has been found to be desirable to initiate movement of the vehicle under actual driving conditions. In particular, a high rate of change in the early range of throttle movement renders engine speed response more sensitive to pedal position than is desirable to comfortably accommodate small changes in vehicle velocity at the low range of throttle movement.
One way in which the rate of change of fluid flow through the throttle body in the early range of throttle movement can be reduced is by reducing the cross-sectional area of the throttle body passage. Unfortunately, a disadvantage of the reduction of the diameter or cross-sectional area of the throttle body passage is that the maximum rate of fluid flow through the passage is limited. Another previously known apparatus used with large area throttle passages is a mechanical linkage between the actuator and the throttle valve to reduce the sensitivity of the fluid flow to pedal actuation in the lower range of throttle movement. However, such linkages require the design, production and assembly of numerous components. Such a mechanism varies the amount by which a throttle plate angle is changed in response to displacement of the throttle actuator or accelerator pedal. Such mechanisms substantially increase the cost and complexity of producing and repairing the motor vehicle.
A diagrammatic example of such a linkage is shown in FIG. 1. The figure illustrates only a general relationship of the numerous links and connections necessary to control movement of the throttle plate 12 in the desired manner and does not disclose the numerous details of the components including such parameters as shaping, clearances and manufacturing tolerances, or the modifications of environmental structures, which must also be taken into account to build and mount or package the linkage in an operable manner on the vehicle. Nevertheless, the diagram is adequate for purpose of demonstrating the general operation and structure of the prior art device for comparison with the present invention.
In FIG. 1, an actuator 11 is shown in solid line at the closed throttle extreme of its range of movement. The actuator is connected to one end of a pivoted bellcrank 14. The other end of the bellcrank 14 is pivotally coupled to a connecting link 16. The connecting link 16 is in turn pivotally connected to a throttle lever 18. The throttle lever 18 is coupled to the valve plate 1 to control its angular orientation within the throttle passage. As shown in solid line in FIG. 1, positioning of the bellcrank 14 at position A results in positioning of the valve plate 12 at a closed throttle position A'. Displacement of the actuator 11 through one-quarter of its range of movement repositions the bell crank to a position B at which the linkage 10 angularly displaces the valve plate 12 only a small amount to the position shown at b'. The linkage 10 mechanically translates movement of the actuator through one-quarter of its range into a small angular displacement of the plate 12, for example, three and one-half degrees from the closed throttle position rather than one-quarter of a full 77.degree. range. Further displacement of the actuator to the half-way point of its range movement reorients the bell crank 14 to the position C shown in FIG. 1, whereby the throttle plate 12 moves to the position C', for example, approximately 18.degree. from the position B'. Movement of the actuator to a position at three-quarters of its full range orients the bellcrank 14 at the position D, thereby displacing the throttle plate 12 to the position D' approximately eighteen and one-half degrees away from position C'. Finally, full actuation of the throttle actuator through its full range of movement reorients the bell crank 14 to the position E, whereby the linkage orients the throttle plate 12 at a wide open throttle position, for example, twenty two and one-half degrees beyond the position D'.
Although modifications of the shape of the throttle passage have been known, none of the passageway modifications disclosed in the prior art particularly address the problem of reducing sensitivity of pedal actuation at the low range of throttle movement. One previously known configuration for throttle body construction is disclosed in U.S. Pat. No. 4,391,247 to Shioyama et al. This patent discloses a throttle body profile used in conjunction with a variable resistor to form a simple sensor in which the resistance varies sufficiently throughout the frequently used low throttle settings. The throttle body passage is profiled so that the wall maintains predetermined distances from the throttle valve path throughout the initial or low range of angular displacement of the throttle valve. While the profile conforms generally with the path to reduce the rate of change of fluid flow past the throttle valve in the frequently used low range, the patent teaches that the resulting reduction in accelerator sensitivity is undesirable. Consequently, the patent specifically teaches a device to compensate for this desensitization of the accelerator pedal.
In addition, the throttle wall profiles disclosed by Shioyama have the disadvantageous effect of reducing the maximum flow rate through the throttle body passage. Furthermore, the profile constructions of the throttle body walls are difficult to construct. For example, the profiles include a negative draft which would render die casting of the device difficult if not impossible by simple molds. Alternatively, the offset profile would require plunge and traverse type machining operations to construct a throttle body profile as shown at FIG. 4 in the patent.
Another known modification of throttle body wall profiles is shown in U.S. Pat. No. 3,047,277 to Landrum. This patent discloses a throttle body construction in which idling jets discharge fuel into the passage on one side of the passage. A portion of the peripheral wall of the throttle passage shrouds the throttle valve to restrict the flow of fluid on the other side of the throttle valve and force the fluid to flow only along the side carrying the idling jets of the passage. This patent teaches that by restricting the fluid flow to the area adjacent the fuel jets, the patented invention provides greater vaporization and mixture of the fuel and air so as to increase fuel economy. This disclosure does not contemplate or address any desensitizing of a throttle actuator throughout the low range of throttle movement. In addition, the wall profile disclosed by the patent restricts the maximum available flow rate through the throttle passage.
Another throttle passage profile construction is disclosed in U.S. Pat. No. 4,474,150 to Foley et al. Foley et al. teaches that recesses can be formed in the throttle passage walls to shroud the throttle plate during the low range of throttle movement from the closed throttle position. The profile is particularly configured at opposite edges of the throttle plate to permit greater than 90.degree. displacement of the throttle plate. Like the apparatus disclosed by Shioyama, Foley et al. teaches that the apparatus will permit simplified calibration of a valve position sensor used for engine control. While purporting to simplify the construction of a modified wall profile in a throttle body, Foley et al. teaches a particular tool which must be used with a complicated machining apparatus such as plunge and traverse machines in order to provide the wall recesses. Furthermore, the recesses are not symmetrical along the longitudinal axis of passage and require two separate plunge and traverse machining operations to form the recesses in the diametrically opposed walls of the throttle body passage.